The growth cycle of hair for human comprises three major phases: anagen (growth phase), catagen (recession phase), and telogen (rest phase), as illustrated in FIG. 1A. In the anagen phase, the derma papilla within the hair bulb receives nutrients and oxygen from the strong blood flow and nourishes the hair follicle for hair growth. Inside the bulb surrounding the papilla, hair cells divide rapidly, much faster than the other cells in the human body, resulting in hair growth. The keratin, leftover protein of dead hair cell, are forced upwards as new cells grow beneath them, so that hair length is extended. In normal circumstance, about 90% of hair follicles are in the anagen phase at any given time. The length of the anagen phase is usually about two to seven years, which determines the maximum hair length. After the anagen phase, signals from the scalp skin instruct to cut down the blood supply to the follicles, forming a club hair detached from the papilla, termed the catagen phase. This phase is a transition phase which is usually relatively short and lasts about two weeks. In the final phase, telogen, the club hair rests and ready to be shed. About 10% of hair follicles are in this phase, which lasts around 3 months under a healthy condition. The transition from telogen to anagen happens when quiescent stem cells at the base of the telogen follicle, near the derma papilla, are activated to induce hair cell proliferation.
Dihydrotestosterone (DHT) is a bi-product of a hormone, which can appear in the men's and women's hair follicles. Androgenic Alopecia (male pattern baldness) is caused by the existence of DHT and the hair follicles sensitive to it. The DHT in the papilla disrupts the normal process of nutrients being absorbed by reducing blood flow and suppresses cell proliferation in the follicles, which shortens the anagen phase, prolongs the telogen phase, and shrinks the size of follicles. This triggers the start of the miniaturization until the follicles eventually reach the vellus stage, in which hair is short, thin, very fine, and hardly visible, although still alive with cycles through the three phases, as illustrated in FIG. 1B.
Currently, there are three types of major products/treatments for treating this condition with approval from Food and Drug Association in the United States. (1) Minoxidil is topical medicine applied to the scalp twice a day, for cutting off DHT around the scalp area. However, using this drug, only around ¼ of men and ⅕ of women experience some hair regrowth within 2 to 4 months. Side effects include oiliness, dryness, or irritation of the scalp. It may also cause unwanted facial hair growth for women. Once the drug application is discontinued, the gained hair will be lost with the possibility of losing more hair. (2) Oral finasteride, taken once daily, blocks the formation of DHT. Side effects include diminished libido and sexual dysfunction. The finasteride has little effect in accelerating the hair restoration, but to prevent further hair loss from DHT. Yet, once the intake of drug is discontinued, DHT is formed again and causes hair loss. (3) Low level laser therapy, utilizing visible red light, delivers light energy to the scalp to increases the amount of adenosine triphosphate (ATP) produced by mitochondria, promoting cellular activity for hair growth. This therapy is suitable for men and women who are in the early stage to the hair loss. The efficacy of the product relies on the sufficient number of follicles without significant miniaturization, but has little effect on miniaturized follicles.
Shock waves are propagating pressure pulses in elastic media, such as air, water and human/animal tissue. Acoustic shock waves have been used for various medical purposes as a noninvasive and non-surgical treatment. It has been proven to be effective to treat a variety of medical conditions in various clinical practices and research reports. For example, in urology, high-intensity focused shock waves are used for breaking kidney/bladder/urethra stones into small fragments on the order of several millimeters in diameter (i.e., lithotripsy), so that the small pieces can be transported out of the patient's body through the urethra. In orthopedics, shock waves are used for pain and inflammation relief/curing in joints and healing of bones. In more recent developments, low-intensity shock waves are found to be effective in modulation of various mechanisms, depending on different types of tissues and conditions. These effects include angiogenesis, nerve regeneration, anti-inflammation, and the induction and acceleration of cell proliferation and stem cell recruitment.
Acoustic shock wave generation is often based on three different mechanisms: electrohydraulic, electromagnetic, and piezoelectric. In the electrohydraulic method (see, e.g., U.S. Pat. No. 4,539,989, incorporated herein by reference), a pulse electric discharge between two closely positioned electrodes inside water induces a sudden vaporization of small amount of water nearby. This rapid increase of volume caused by the vaporization creates a pressure pulse in the water, thus generates radial propagating shock waves. In the electromagnetic method (see, e.g., U.S. Pat. No. 5,174,280, incorporated herein by reference), an electric current pulse in a conductor coil results in a pulsed electromagnetic field, which in turn repels a conductive film having certain elastic properties and positioned closely to the coil, thereby generating a momentary (e.g., pulsed) displacement in the conductive film. The momentary displacements in turn generate shock waves with wave fronts parallel to the metal film surface. Alternatively, in the piezoelectric shock wave generation method (see, e.g., U.S. Pat. No. 5,119,801, incorporated herein by reference), electrical voltage pulses are applied to an array of piezoelectric ceramic tiles. The voltage pulses induce volume expansions and contractions of the ceramics with each, thereby generating shock waves with wave fronts parallel to the ceramic surfaces.